U.S. patent number 4,912,210 [Application Number 07/244,355] was granted by the patent office on 1990-03-27 for process for the preparation of (cyclo)aliphatic uretediones.
This patent grant is currently assigned to Huels Aktiengesellschaft. Invention is credited to Josef Disteldorf, Werner Huebel, Karl Schmitz.
United States Patent |
4,912,210 |
Disteldorf , et al. |
March 27, 1990 |
Process for the preparation of (cyclo)aliphatic uretediones
Abstract
A process for the preparation of a uretedione, comprising the
steps of: (i) reacting at least one C.sub.6-15 (cyclo)aliphatic
diisocyanate under substantially anhydrous conditions with a
pyridine of the formula ##STR1## wherein R.sub.1 and R.sub.2 are,
independent from one another, a C.sub.1-4 alkyl group or R.sub.1
and R.sub.2 taken together with the attached nitrogen form a
pyrrolidine, piperidine or morpholine ring, to form a reaction
mixture containing said uretedione, and (ii) isolating said
uretedione from said reaction mixture by vacuum thin layer
evaporation after the degree of dimerization in said reaction
mixture has reached 10-80%.
Inventors: |
Disteldorf; Josef (Marl,
DE), Huebel; Werner (Recklinghausen, DE),
Schmitz; Karl (Gladbeck, DE) |
Assignee: |
Huels Aktiengesellschaft (Marl,
DE)
|
Family
ID: |
6341000 |
Appl.
No.: |
07/244,355 |
Filed: |
September 15, 1988 |
Foreign Application Priority Data
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Nov 21, 1987 [DE] |
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3739549 |
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Current U.S.
Class: |
540/202 |
Current CPC
Class: |
C07D
229/00 (20130101); C08G 18/798 (20130101) |
Current International
Class: |
C07D
229/00 (20060101); C08G 18/00 (20060101); C08G
18/79 (20060101); C07D 229/00 (); C07D 213/4 () |
Field of
Search: |
;540/202 |
Foreign Patent Documents
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3420113 |
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May 1985 |
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DE |
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1207673 |
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Oct 1970 |
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GB |
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Primary Examiner: Shah; Mukund J.
Assistant Examiner: Cseh; C. L.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt
Claims
What is new and desired to be secured by letters patent of the
United States is:
1. A process for the preparation of a uretedione, consisting
essentially of the steps of:
(i) reacting a C.sub.6-15 (cyclo)aliphatic diisocyanate under
substantially anhydrous conditions with a pyridine of the
formula
wherein said pyridine is used in a quantity ranging from 0.05-10%
by weight relate to the diisocyanate wherein R.sub.1 and R.sub.2
are, independently from one another, a C.sub.1-4 alkyl group or
R.sub.1 and R.sub.2 taken together with the attached nitrogen form
a pyrrolidine, piperidine or morpholine ring, to form a reaction
mixture containing said uretedione, and
(ii) isolating said uretedione from said reaction mixture by vacuum
thin layer evaporation after the degree of dimerization in said
reaction mixture has reached 10-80%.
2. The process of claim 1, wherein said uretedione isolated from
said reaction mixture is more than 99% pure.
3. The process of claim 1, wherein said isolating step is conducted
after the degree of dimerization in said reaction mixture has
reached 20-60%.
4. The process of claim 1, wherein 0.2-5% by weight of said
pyridine is used.
5. The process of claim 1, wherein R.sub.1 and R.sub.2,
independently, are a methyl or ethyl group.
6. The process of claim 1, wherein said reacting step is conducted
at a temperature from about 0.degree.-100.degree. C.
7. The process of claim 6, wherein said reacting step is conducted
at a temperature from about 20.degree.-80.degree. C.
8. The process of claim 1, wherein said vacuum thin layer
evaporation is performed at a vacuum ranging from about 0.1 to 20
mbar and at a temperature ranging from about
150.degree.-190.degree. C.
9. The process of claim 1, wherein the distillate obtained by said
vacuum thin layer evaporation comprises said diisocyanate and said
pyridine and wherein said distillate is recycled to said reacting
step.
10. The process of claim 1, wherein said reacting step is conducted
in inert gas atmosphere.
11. The process of claim 1, wherein said diisocyanate is a
C.sub.8-12 (cyclo)aliphatic diisocyanate.
12. The process of claim 1, wherein said diisocyanate is selected
from the group consisting of hexamethylene diisocyanate,
dodecamethylene diisocyanate, bis(4-isocyanatocyclohexyl)-methane,
2-methylpentamethylene diisocyanate, 2,2,4-trimethylhexamethylene
diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate and
isophorone diisocyanate.
13. The process of claim 1, wherein said diisocyanate is isophorone
diisocyanate.
14. The process of claim 1, wherein said reacting step is conducted
in the presence of an inert solvent.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is related to an improved process for the preparation
of largely isocyanurate-free uretediones from (cyclo)aliphatic
diisocyanates. Such uretediones can be processed into light-fast,
single and two component polyurethane paints. The presence of
isocyanurates is undesired in a number of applications since, as
well-known, they are trifunctional and have a tendency to form
crosslinkages. In practice an admixture of more than 0.5% is
regarded as undesirable.
2. Discussion of the Background
In principle it is well-known that uretediones can be prepared in
the presence of specific catalysts through dimerization of
isocyanates. Previously for this purpose antimony pentafluoride,
trialkylphosphines, amino-substituted phosphines, imidazoles,
guanidines, and pyridines have been proposed.
The drawback in the use of antimony pentafluoride (cf. DE-OS No. 34
20 114) is that this corrosive and expensive compound must be
destroyed prior to distillation with a five-fold quantity of zinc
powder and the antimony and zinc fluoride precipitate must be
removed by means of filtration.
A process is known from FR-PS No. 15 32 054 in which tertiary
phosphines or boron trifluoride are added as dimerization
catalysts. However, they catalyze not only the dimerization but
also to a significant degree also the trimerization of isocyanates.
In addition to this, due to its high corrosiveness, boron
trifluoride can be added only when specific protective measures are
taken.
1,2-Dimethylimidazole is an excellent dimerization catalyst for
aromatic isocyanates (cf. Synthesis 1975, p. 463 ff.). However, in
the case of isocyanates that do not have any aromatic NCO groups,
this catalyst is clearly less selective. For example, when benzyl
isocyanate is added, a mixture of 24% isocyanurate and only 76%
uretedione is obtained.
In practice amino-substituted phosphines have prevailed as
dimerization catalysts.
According to the process of DE-OS No. 30 30 513, the uretedione of
the isophorone diisocyanate is prepared in the presence of an
organic phosphorus-nitrogen-catalyst by means of dimerization of
monomers and then distilled in a thin-layer evaporator. The
uretediones remain in the distillation residue while the
unconverted monomers with the majority of the added catalyst are
collected as distillate, which is recycled into the process.
Tris-(N,N-dimethylamino)-phosphine (PTD) is designated as the
preferred catalyst. Uretediones, which were produced in the
presence of PTD, contain typically 1% isocyanurate, 1% monomers,
and 0.01-0.1% catalyst.
In the DE-OS No. 34 47 635 it is proposed that for the dimerization
of organic isocyanates the same type of catalysts be used with
concurrent use of active hydrogen containing organic compounds such
as alcohols, phenols, (cyclo)aliphatic amines, amides, urethanes,
and ureas. PTD and tris-(N,N-diethylamino)-phosphine are
particularly preferred catalysts. If di- or higher functional
isocyanates are added, the reaction usually stops after attaining a
degree of dimerization ranging from 10 to 50% due to the addition
of a catalyst poison such as chloroacetic acid (cf. page 16, first
paragraph). Isolating the uretedione presents a problem. Under the
conditions of thin-layer evaporation there is the risk of a
catalyzed dissociation of the uretedione that is present back to
the original isocyanates (cf, page 16, middle). If the catalyst
with the excess isocyanate can be removed by means of distillation,
deactivation of the catalyst is superfluous. However, then
uncontrollable secondary reactions can occur during and after
work-up (cf, page 20).
It is known that PTD has a tendency to react in the presence of
atmospheric oxygen to form hexamethyl triamidophosphoric acid,
which as is well-known, is suspected to be a carcinogen (cf.
Br.J.Cancer 38, 418-427 (1978)). Therefore, the use of PTD should
be avoided. In addition to this, the aforementioned processes have
the drawback that the catalysts enter into secondary reactions and
thus are partially consumed. Therefore, in these processes, the
lost catalyst must be regularly replaced. In the latter processes,
a significant proportion of the catalyst thus employed remains in
the uretedione after the deactivation. Therefore, a drawback of
both processes is the high cost of the catalyst.
Other dimerization catalysts are also known from the literature.
For example, in the JP-AS No. 71/37 503 the dimerization of
2,4-toluylene diisocyanate with cyclic amidines such as
1,8-diazabicyclo[5.4.0]undec-7-en is described. Experiments
conducted by the Applicant show that (cyclo)aliphatic diisocyanates
cannot be dimerized with this catalyst (see reference example A).
Apparently the well-known, low reactivity of these diisocyanates is
inadequate to facilitate a reaction.
The object of DE-PS No. 10 81 895 (corresponding to U.S. Pat. No.
3,144,452) is a process for the preparation of
N,N-diaryluretediones and triarylisocyanurate acid esters through
di- or trimerization of aromatic isocyanates. Pyridines containing
a substituent in the 3- or 4-position and of a specified basicity
are used as catalysts. Among other things, 4-aminopyridines that
are substituted by means of alkyl groups are mentioned. According
to this process, it is apparently possible to obtain uretediones,
isocyanurates or their mixtures, depending on the quantity of the
catalyst, the reaction temperature, and type of solvent that is
used. Thus, for example, it is recommended that for the production
of uretediones the catalyst be added in a quantity ranging from
0.005 to 15%, with respect to the weight of the isocyanate added,
the mixture be reacted at the lowest temperature possible, and an
inert organic solvent be used in which the uretedione dissolves
poorly.
The fact that the quantity of catalyst recommended for the
preparation of isocyanurates overlaps in broad ranges the
aforementioned data and the other two reaction parameters are also
not clearly delineable, leads one skilled in the art to doubt the
possibility of controlling a selective reaction. Reference
experiments conducted by the Applicant show in fact that the two
oligomers are always formed. For example, in the follow-up of
Example 2, 2% by weight of isocyanurate was obtained. If the
reaction mixture is heated briefly to 145.degree. C., even 10% by
weight of isocyanurate is obtained, whereas at the same time the
uretedione is partially split into the monomer.
It is evident from a later application of the patent holder that
4,4'-diphenylmethane-diisocyanate is trimerized in the presence of
4-dimethylaminopyridine at room temperature and is converted to
higher oligomeric products (cf. DE-AS No. 16 94 485). From this,
too, it can be inferred that apparently the pyridine derivatives
always catalyst both reactions--the dimerization and the
trimerization. Therefore, pyridine derivatives do not seem to be
suitable for the preparation of uretediones, which should be almost
free of isocyanurates. In particular, this applies to aliphatic
isocyanates, since in contrast to the aromatic isocyanates, they
form either no uretediones or only when special reaction conditions
are maintained are they in a position to form the dimeric addition
products (cf. J.Org.Chem. 36, 3056 (1971)).
Therefore, whereas numerous processes for the dimerization of
aromatic diisocyantes are known, there is practically only one
possibility for dimerizing (cyclo)aliphatic diosocyanates; and it
is based on the use of undesired aminophosphines (see DE-OS No. 34
37 635)).
The process described in JP-OS No. 84/98180 for the oligomerization
of (cyclo)aliphatic diisocyanates is not suitable for the targeted
preparation of uretediones, since it is known that the mixtures
obtained comprising uretediones and isocyanurates are separable
only with great difficulty. Uretediones have the tendency, on
heating to reseparate back into their original components. In
particular, this can be expected when catalyst residues are still
present.
SUMMARY OF THE INVENTION
Thus one object of the present invention is to provide a process
for catalytic preparation of (cyclo)aliphatic uretediones with more
than 99% purity, which is independent of the use of expensive and
potentially carcinogen aminophosphines.
This and other objects which will become apparent from the
following specification have been achieved by the present process
for the preparation of a uretedione which comprises the steps
of:
(i) reacting at least one C.sub.6-15 (cyclo)aliphatic diisocyanate
under substantially anhydrous conditions with a pyridine of the
formula ##STR2## wherein R.sub.1 and R.sub.2 are, independently
from one another, a C.sub.1-4 alkyl group or R.sub.1 and R.sub.2
taken together with the attached nitrogen form a pyrrolidine,
piperidine or morpholine ring, to form a reaction mixture
containing said uretedione, and
(ii) isolating said uretedione from said reaction mixture by vacuum
thin layer evaporation after the degree of dimerization in said
reaction mixture has reached 10-80%.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Surprisingly, such a process has now been found. It comprises
dimerizing an aliphatic and/or cycloaliphatic diisocyanate
containing 6 to 15 carbon atoms in the presence of a pyridine of
the general formula: ##STR3## in which R.sub.1 and R.sub.2 denote
independently from one another an alkyl group having 1 to 4 carbon
atoms or together with the nitrogen can form a pyrrolidine ring,
piperidine ring, or a morpholine ring; and after reaching a degree
of dimerization of 10 to 80%, preferably 20 to 60%, the reaction
mixture is subjected to vacuum thin-layer evaporation in order to
isolate the uretedione. Thus, it is not necessary to stop the
reaction by adding a catalyst poison. Isophorone diisocyanate is
preferred as a diisocyanate. The substituted pyridine, in
particular p-dimethylaminopyridine, is added in a quantity ranging
from 0.05 to 10% by weight, preferably from 0.2 to 5% by weight.
Dimerization is preferably performed at a temperature between
0.degree. to 100.degree. C., the thin-layer evaporation depending
on the attached vacuum ranging from 0.1 to 20 mbar at a temperature
from 150.degree. to 190.degree. C. The distillate of the thin-layer
evaporation can be recycled again. It is preferable that the
dimerization be performed in the presence of an inert protective
gas to provide an anhydrous atmosphere.
Thus of the substituted pyridines disclosed in DE PS No. 10 81 895,
only the 4-dialkylaminopyridines are suitable as dimerization
catalysts. Based on prior art, it is surprising that these
pyridines are highly selective catalysts for the dimerization of
(cyclo)aliphatic diisocyanates.
It is remarkable that according to this process uretediones are
obtained in high purity. On the basis of prior art reference one
would have expected that during the reaction a specific proportion
of isocyanurates would already be formed. The vacuum thin-layer
evaporation requires only a short period of time at temperatures up
to a maximum of 190.degree. C. Even under these temperature
conditions which, for uretediones are drastic, no significant
quantity of isocyanurates is formed. In the process of the
invention the total percentage of isocyanurate formed is thus below
0.5%, with respect to the total quantity of uretedione produced at
the same time.
It is also advantageous that the substituted pyridines that are
required as catalysts are readily available commercial
products.
Finally, the course of the reaction is significantly easier to
control with the use of substituted pyridines since almost no
secondary reactions take place.
By "(cyclo)aliphatic" is meant aliphatic and cycloaliphatic
diisocyanates having 6 to 15 carbon atoms, preferably 8 to 12
carbon atoms. For example, hexamethylene diisocyanate,
dodecamethylene diisocyanate and
bis(4-isocyanatocyclohexyl)-methane and their mixtures are suitable
for use as the diisocyanates. Preferred aliphatic diisocyanates are
2-methylpentamethylene diisocyanate, as well as 2,2,4- and
2,4,4-trimethylhexamethylene diisocyanate. Among the cycloaliphatic
diisocyanates, isophorone diisocyanate is preferred.
The pyridine used as dimerization catalyst has the general formula:
##STR4##
R.sub.1 and R.sub.2 denote, independently of one another, an alkyl
group having 1 to 4 carbon atoms or together with the neighboring
nitrogen atom form a pyrrolidine, piperidine, or morpholine ring.
Excellent results are achieved with p-pyrrolidinopyridine (see
Tables 4 and 5). However, due to their better availability,
4dimethylaminopyridine and/or 4-diethylaminopyridine are preferred
as catalysts. The catalyst is added in a quantity ranging from 0.5
to 10%, in particular from 0.2 to 5%, with respect to the parts by
weight of the diisocyanate added.
The dimerization can be performed in the presence of solvents,
which are inert with respect to diisocyanates. Of course, as a rule
such a variation of the process does not exhibit any special
advantages. In particular hexane, toluene, xylene, chlorobenzene
and their mixtures are suitable.
The reaction temperature normally ranges from about 0.degree. to
100.degree. C., preferably from about 20.degree. to 80.degree. C.
It is advantageous to perform the dimerization in the presence of a
protective inert gas atmosphere such as nitrogen, argon, etc. to
provide substantially androus conditions. The reaction may be
carried out at normal atmospheric pressure. The reaction times
generally range from 1 to 5 days, and depend primarily on the
concentration of the catalyst.
As soon as a degree of dimerization has reached from 10 to 80%,
preferably from 20 to 60%, the reaction feedstock is subjected
directly to a vacuum thin-layer evaporation. Thus it is
advantageous to forego the deactivation of the catalyst. With
thin-layer evaporation for the purpose of preparing IPDI
uretedione, the temperature is set, in particular, at 180.degree.
C. and the pressure is set at 0.55 mbar in the preevaporator. In
the main evaporator the temperature is, in particular, 165.degree.
C. and the pressure is 0.05 mbar. The dwell time in the
pre-evaporator and the main evaporator is then approximately 1
minute respectively.
In the vacuum thin-layer evaporator more than 99% pure uretedione
is recovered as the distillation residue. The monomer content is
determined by means of gas chromatography. The final product
contains less than 0.5% isocyanurate; the monomer content is below
0.4%; catalyst residues are not detectable.
The distillate comprises monomer diisocyanate and catalyst. It is
preferable to recycle the distillate to the dimerization
process.
The degree of dimerization was determined using the NCO number and
the course of the reaction was observed with the aid of the NCO
number. The NCO number is determined according to the method
described in Houben-Weyl "Methoden der Organischen Chemie", Vol.
14/2, Stuttgart (1963), p. 85.
The isocyanurate content in the reaction product is determined
qualitatively using IR spectroscopy and quantitatively by
determining the thermal value of NCO. In order to determine the
thermal value of NCO, the sample is boiled in dichlorobenzene for 2
hours. Then the NCO number is determined in the conventional
manner.
Having generally described this invention, a further understanding
can be obtained by reference to certain specific examples which are
provided herein for purposes of illustration only and are not
intended to be limiting unless otherwise specified.
EXAMPLES
EXAMPLE 1
A 100 g sample of a (cyclo)aliphatic diisocyanate, which contains
1% by weight of p-dimethylaminopyridine, was maintained at
70.degree. C. under nitrogen for 24 hours. Then the degree of
dimerization was determined. Table 1 shows the values which were
obtained.
TABLE 1 ______________________________________ Degree of
(Cyclo)aliphatic diisocyanate Dimerization
______________________________________
2-methylpentane-1,5-diisocyanate 33.8% isomer mixture comprising
2,2,4- and 25.6% 2,4,4-trimethylhexamethylene diisocyanate
hexane-1,6-diisocyanate 29.9% isophorone diisocyanate 26.6%
______________________________________
EXAMPLE 2
100 g Samples of isophorone diisocyanate, which contain varying
quantities of p-dimethylaminopyridine, were left standing at room
temperature under nitrogen for 1 to 5 days. Then the degree of
dimerization was determined, as shown in Table 2.
TABLE 2 ______________________________________ Parts by weight of
Degree of p-dimethylamino- dimerization Example pyridine (%) after
1 day after 5 days ______________________________________ 2.1 0.5
11.1% 33.3% 2.2 1.0 28.6% 49.2% 2.3 2.0 33.9% 61.9% 2.4 5.0 55.0%
74.1% ______________________________________
EXAMPLE 5
Samples of isophorone diisocyanate, which contain varying parts by
weight of p-dimethylaminopyridine, were left standing at room
temperature under nitrogen. Then distillative work-up was performed
in a vacuum thin-layer evaporator. Table 3 shows the test results
that were obtained.
TABLE 3 ______________________________________ Example Example
Example 3.1 3.2 3.3 ______________________________________
isophorone diisocyanate 2.97 2.94 2.85 feedstock (kg)
p-dimethylaminopyridine 1.0 2.0 5.0 (% by wt.) reaction time
(hours) 120 67 17.5 distillate 57.3 58.2 63.1 (% by weight of
feedstock) uretedione yield 42.7 41.8 36.9 (% by weight of
feedstock) ______________________________________
EXAMPLE 4
A 100 g sample of isophorone diisocyanate, which contains 5% by
weight of dimerization catalyst, was maintained at room temperature
under nitrogen for 1 day. Then the degree of dimerization was
determined, as shown in Table 4.
TABLE 4 ______________________________________ Example Catalyst
Degree of Dimerization ______________________________________ 4.1
p-pyrrolidinopyridine 61.4% 4.2 p-diethylaminopyridine 55.0% 4.3
p-piperidinopyridine 50.3% 4.4 p-morpholinopyridine 16.9%
______________________________________
EXAMPLE 5
A 100 g sample of isophorone diisocyanate, which contains 1% by
weight of dimerization catalyst, was maintained at room temperature
under nitrogen for 2 days. Then the degree of dimerization was
determined, as shown in Table 5.
TABLE 5 ______________________________________ Example Catalyst
Degree of Dimerization ______________________________________ 5.1
p-pyrrolidinopyridine 48.1% 5.2 p-diethylaminopyridine 48.1% 5.3
p-dimethylaminopyridine 39.7% 5.4 p-piperidinopyridine 30.2%
______________________________________
Reference Examples A to D
A 100 g sample of isophorone diisocyanate, which contains 1% by
weight of dimerization catalyst, was maintained at room temperature
under nitrogen for 1 to 10 days. Then the degree of dimerization
was determined, as shown in Table 6.
TABLE 6 ______________________________________ Reference Degree of
Dimerization Example Catalyst 1 day 10 days
______________________________________ A 1,8-diazabicyclo[5.4.0]- 0
0 undec-7-ene B 1,2-dimethylimidazole 0 0 C 3-dimethylaminopyridine
0 0 D 2-dimethylaminopyridine 0 0
______________________________________
Obviously, numerous modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *